1. Field of the Invention
The present invention relates to a vibrator driving method and a vibrating apparatus. In particular, the present invention relates to a vibrating apparatus which is used in a foreign substance removing apparatus of an optical apparatus such as a camera, a facsimile apparatus, a scanner, a projector, a copying machine, a laser beam printer, an inkjet printer, a lens, binoculars, an image displaying apparatus or the like, and a driving apparatus which drives an object by vibration.
2. Description of the Related Art
In recent years, with improvement of resolution of an optical sensor in an image pickup apparatus, an adverse influence of a foreign substance adhering to an optical system during operation of the apparatus, on a picked-up image, has come to be considered increasingly serious.
In particular, since the resolution of an image pickup element used in a video camera or a still camera has been remarkably improved, a defect in image arises if the foreign substance adheres to an optical component disposed in the vicinity of the image pickup element.
For example, if a foreign substance such as dust from outside the apparatus or abrasion powder produced on a mechanical sliding surface within the apparatus adheres to an infrared cut filter, an optical low-pass filter or the like, the foreign substance is taken in a picked-up image since an image rarely blurs on the surface of the image pickup element.
On another front, an image pickup unit of a copying apparatus, a facsimile apparatus, a scanner or the like reads a plane original by causing a line sensor to perform scanning or scanning an original brought close to the line sensor.
In this case, if a foreign substance adheres to a light ray incident unit of the line sensor through which light enters the line sensor, the foreign substance is taken in a scanned image.
In a so-called moving original reading method in which an original is read during conveyance from a reading unit of an original scanning apparatus, a reading unit of a facsimile apparatus, or an automatic document feeder of a copying apparatus, one foreign substance is taken as a linear image which extends in an original feeding direction. Thus, a problem of degrading image quality is caused.
The image quality can be recovered by manually wiping off the foreign substance. However, a foreign substance which adheres to the light ray incident unit during an operation of the apparatus cannot be recognized until after an image has been picked up.
Namely, if the image is picked up or scanned before the foreign substance is wiped off, an image of the foreign substance is taken in the picked-up image, whereby image correction by software is required. Besides, in the case of a copying machine, such an image is output onto a paper medium simultaneously, whereby it takes a great deal of labor to correct the image.
To solve this kind of problem, a foreign substance removing apparatus which moves a foreign substance from an image reading unit by giving a vibration, and an optical apparatus which is equipped with the relevant foreign substance removing apparatus have been proposed conventionally (United States Patent. Application Publication US2009/0207493.)
FIG. 11A is a diagram illustrating a constitution of a vibrating apparatus provided in the conventional foreign substance removing apparatus disclosed in United States Patent. Application Publication US2009/0207493.
A vibrating apparatus 300 is provided on an image pickup apparatus 301 which converts an object image received into an electrical signal to thereby generate image data.
A space formed on the front surface of the image pickup apparatus 301 is hermitically sealed by the vibrating apparatus 300 and the image pickup apparatus 301.
The vibrating apparatus 300 includes a rectangular-plate optical element 302, and a pair of piezoelectric elements 303a and 303b which act as electromechanical energy conversion elements and are rigidly glued to respective opposite ends of the optical element.
An alternating voltage Va is applied to the piezoelectric element 303a, and an alternating voltage Vb is applied to the piezoelectric element 303b. 
In FIG. 11B, a waveform A indicates a displacement distribution of a first-order out-of-plane bending vibration, and a waveform B indicates a displacement distribution of a second-order out-of-plane bending vibration.
The axis of ordinate indicates the out-of-plane displacement of the surface of the vibrating apparatus 300 opposite to the surface on which the image pickup apparatus 301 is arranged, and the direction toward the side of the image pickup apparatus 301 is set to be negative. On the other hand, as illustrated in the drawing, the axis of abscissa corresponds to the locations of the vibrating apparatus 300 in the longitudinal direction.
Each of the alternating voltages Va and Vb is the alternating voltage of which the period has a response of the resonance phenomenon and the first-order out-of-plane bending vibration and the second-order out-of-plane bending vibration. Further, the time phases of the alternating voltages Va and Vb are different from each other.
Thus, a vibration which is obtained by combining the two vibrations of the first-order out-of-plane bending vibration and the second-order out-of-plane bending vibration respectively having the different time phases is excited in the vibrating apparatus 300.
FIGS. 12, 13, 14 and 15 are graphs indicating respective displacements and displacement speeds of the first-order out-of-plane bending vibration and the second-order out-of-plane bending vibration in a case where the time phase difference between the two vibrations is set to 90° and the amplitudes of the two vibrations are set to be 1:1, and displacements and displacement speeds of the vibrator resulting from superposition of the two vibrations, on a time phase-by-time phase basis.
In each of these drawings, the axis of ordinate indicates the displacement and the displacement speed, and the direction toward the side of the image pickup apparatus 301 is set to be negative. On the other hand, as well as FIG. 11B, the axis of abscissa corresponds to the locations of the vibrating apparatus 300 in the longitudinal direction.
In the drawings, a waveform C represents the displacement of the first-order out-of-plane bending vibration, and a waveform D represents the displacement of the second-order out-of-plane bending vibration. A waveform E represents the displacement of the vibrator 300 resulting from superposition of the two vibrations. A waveform G represents the displacement of the vibrator 300 in a 30° earlier time phase than the time phase of the waveform E. A waveform F represents the normalized displacement speed of the vibrator 300.
In a case where the foreign substance removing apparatus is operated, when the optical element 302 thrusts up a foreign substance out of plane (i.e., in the positive direction on the axis of ordinate in each of FIGS. 12 to 15), the foreign substance on the front surface of the optical element 302 receives a force in the normal direction and is moved in a repelled fashion.
More specifically, if the waveform F indicative of the displacement speed assumes a positive value in each time phase, the foreign substance is thrust up out of plane, and receives a force in the normal direction of the waveform E indicative of the displacement of the vibrating apparatus 300 in this time phase to be moved away. In a case where the displacement is given with the optical element 302 raised at a certain angle (typically in a vertical direction), if the foreign substance on the front surface of the optical element 302 receives the force in the normal direction and is moved away, the moved-away foreign substance does not again adhere to the relevant surface with a fixed probability but falls by gravity.
Each of arrows h in FIGS. 12 to 15 indicates a direction in which the foreign substance moves.
As can be understood from FIGS. 12 to 15, from the location 60 to the location 300 of the optical element 302, an amount of vibration for moving the foreign substance in the positive direction on the axis of abscissa is much larger than an amount of vibration for moving the foreign substance in the negative direction on the axis of abscissa during one period of vibration. Consequently, the foreign substance can be moved in the positive direction on the axis of abscissa.
If the valid portion of the optical element 302 which is valid in regard to the image pickup apparatus 301 is within the range from the location 60 to the location 300, the foreign substance can be removed from the valid portion.
However, such problems as described below arise in the above-described vibrating apparatus. Namely, in United States Patent Application Publication US2009/0207493, since the vibrating apparatus has numerous vibration modes, unnecessary vibration modes other than desired two vibration modes mixedly exist.
Namely, since the unnecessary vibration modes mixedly exist, a place where the in-plane directions at the time when the foreign substance on the front surface of the optical element is thrust up out of plane are opposite to each other, and a place where the component in the in-plane direction is small arise.
Further, in some places, the foreign substances cannot be moved because the in-plane moving directions face to each other, or moving force becomes small in regard to adhesion of the foreign substance. Thus, efficiency of moving the foreign substance lowers.
The present invention, which has been completed in consideration of the above-described problems, aims to provide a vibrator driving method which enables to effectively move an object including a foreign substance in a predetermined direction by vibration, a vibrating apparatus which uses the vibrator driving method, and a driving apparatus, a foreign substance removing apparatus and an optical apparatus each of which has the vibrating apparatus.